A locking power clamp has been developed and disclosed in U.S. Pat. No. 4,458,889 which employs highly pressurized needle bearings in straight track portions of the clamp which actuate links connected to a pivoted clamp arm. In normal use, the clamp is bolted to a rigid fixture or other work support with the clamp arm, actuated by air pressure, adjusted to clamp the workpiece against the reaction surface of the work support. Toggle linkage is adapted to reach a center or slightly overcenter position which locks the arm in clamping engagement subject to retraction by the air cylinder with somewhat less force than the maximum clamping pressure force. This phenomenon of reduced requirement for release pressure is attributable to the use of special needle bearings as critical elements in the toggle linkage.
In a modification of the clamp illustrated in FIGS. 4 and 8 of the drawings, an auxilliary clamp arm is provided to travel in linear relation with the actuating piston rod toward a clamping relationship with the pivoting arm, clamping pressure in such case being limited to the axial force which is applied to the piston rod. With such feature a workpiece may be clamped between the pivoting arm and supplemental arm independent of any reaction base normally employed with a single clamp arm. If the supplemental arm is adapted with a right angle extended arm for parallel clamping relationship with a 180.degree. pivoted arm, the limitation of axial force applied to the piston rod will not exist since the leverage of clamping force exerted against the auxilliary arm will be absorbed by spaced bearings on reaction track surfaces. However, in such case, the final clamping pressure will be exerted by clamping arm surfaces moving in relatively right angle relationship rather than converging on a preferred straight line relationship.